Without seeing how much of the kid is legs, we can't really know about measurements etc. At that age, ask him what he feels comfortable on. Go by feel more than by numbers. You might want to consider getting him a bike from a Toys R Us or a Wal-Mart type store for now. You can always take it to get it checked out, make sure everything is put together correctly etc. The biggest thing is that the kid is growing. As you know, he grows extremely fast. So, a bike a bit big right now, won't be so big in what might even be six months down the road. Of course a dealer is the best way to go, and for that you should just check your local listings. Los Angeles is sure to have tons of them, and I'm sure that most are quite well regarded. In an area with that much competition you have to be. I have noticed that many smaller sized bikes now offer a wider aray of gearing. That shouldn't be a problem. Oh, and at that age a used bike may not be a problem either. I know you'll want new, but you can find some good deals on decent bikes used. As I mentioned earlier with rapid growth this may be a good avenue. That's about all I can think of for now. Sorry if it's a bit of a jumbled mess. Good luck.